These studies are designed to elucidate mechanisms by which macrophages become cytotoxic for tumor cells. In particular, we will be further characterizing the lymphocyte mediator macrophage activating factor (MAF), comparing it to migration inhibitory factor (MIF). We will also be continuing studies of the MAF - macrophage interaction and how it initiates enhancement of macrophage cytotoxicity. Finally, we will continue to develop a method to study the interaction between human monocyte-macrophages and human target cells.